Internal combustion engine exhaust cooling system

ABSTRACT

An internal combustion engine exhaust cooling system includes an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head, and an exhaust branch pipe, and cools exhaust gas that flows through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage. The coolant passage includes a first passage and a second passage being provided according to an offset of an amount of heat received from exhaust gas in a circumferential direction of an inner surface of the exhaust passage, and two middle passages that connect the first passage with the second passage at both ends of the two middle passages, and a coolant delivery direction is a direction from the second passage side of a first middle passage, of the two middle passages, toward the first passage side.

INCORPORATION BY REFERENCE

This application claims priority to Japanese Patent Application No.2010-066974 filed on Mar. 23, 2010, which is incorporated herein byreference in its entirety including the specification, drawings andabstract.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an internal combustion engine exhaust coolingsystem in which an exhaust gas cooling adapter that is arranged betweenan exhaust port that opens in a cylinder head and an exhaust branchpipe, and that cools exhaust gas flowing through an exhaust passage byrunning coolant through a coolant passage formed inside of a wall thatsurrounds the exhaust passage.

2. Description of the Related Art Japanese Patent ApplicationPublication No. 11-49096 (JP-A-11-49096) and Japanese Utility ModelApplication Publication No. 64-15718 (JP-U-64-15718), for example,describe technologies for cooling exhaust gas in order to suppress heatdamage to the internal combustion engine exhaust system. InJP-A-11-49096, a connecting member is provided between a cylinder headand an exhaust branch pipe, and a coolant passage is provided in thisconnecting member. This coolant passage is formed as a concave portion.Coolant introduced from both ends on the lower side of the coolantpassage flows directly into the coolant passage on the exhaust branchpipe side.

In JP-U-64-15718, a first exhaust gas cooling adapter is arrangedbetween a cylinder head and an exhaust branch pipe, and a second exhaustgas cooling adapter is arranged between the exhaust branch pipe and aturbocharger. A coolant passage of the first exhaust gas cooling adapterpasses from an inlet provided on a lower side of one end of anarrangement of exhaust passages corresponding to exhaust ports, throughthe lower side of the arrangement, turns back at the opposite end, andpasses through the upper side of the arrangement, and discharges coolantout from an outlet directly above the inlet. As a result, the exhaustgas that has just come out of the exhaust ports is cooled by the exhaustgas cooling adapter. With the second exhaust gas cooling adapter, acoolant inlet and a coolant outlet are formed on opposite corners of acooling passage formed around a single exhaust passage. This secondexhaust gas cooling adapter runs coolant around the exhaust passage,thus cooling the exhaust gas that has already been cooled by the firstexhaust gas cooling adapter.

Exhaust gas discharged from a combustion chamber of an internalcombustion engine via an exhaust port does not flow uniformly throughthe exhaust passage. That is, the flow of exhaust gas may become unevenor the exhaust gas may bump along due to the shape of the exhaust port,the positional relationship between the exhaust port and an exhaust gascooling adapter that is connected to the exhaust port, or the shape ofthe exhaust gas cooling adapter. As a result, a large difference intemperature may occur at the inner surface of the exhaust gas coolingadapter, which may cause the exhaust cooling performance to decrease.

With the connecting member in JP-A-11-49096, the concave portion thatserves as the coolant passage is provided to supply coolant to theexhaust branch pipe side. Therefore, the shape of the concave portionitself does not sufficiently surround the exhaust passage. Moreover,coolant flows directly out to the exhaust branch pipe side withoutsufficiently flowing into the concave portion, so the function ofcooling the exhaust gas that has been discharged from the exhaust porton the cylinder head side is extremely low. Therefore, this technologydoes not enable the exhaust passage of the exhaust gas cooling adapterto be efficiently cooled.

With the first exhaust gas cooling adapter in JP-U-64-15718, exhaust gasdischarged from the exhaust port of the internal combustion engine iscooled by running coolant uniformly along the entire periphery of theexhaust passage. With such uniform cooling, in order to sufficientlycool the exhaust gas even at a high temperature portion that occurs dueto the temperature difference described above, it is necessary to run anoverall large amount of coolant inside the water jacket of the firstexhaust gas cooling adapter. Such an approach, however, increases thesize of the exhaust gas cooling adapter and increases the load on thewater-jet pump. As a result, the internal combustion engine may becomeheavier and less fuel efficient.

With the second exhaust gas cooling adapter in JP-U-64-15718, cooling issimply performed a second time in order to protect the turbocharger.Cooling is not aimed at the high temperature exhaust gas from theexhaust port. Moreover, the temperature difference described above isnot taken into account, and the flow of coolant is not one that actuallyaddresses the temperature difference.

SUMMARY OF THE INVENTION

The invention thus provides an internal combustion engine exhaustcooling system capable of efficiently cooling an exhaust passage of anexhaust gas cooling adapter without increasing either the size of theexhaust gas cooling adapter or the load on a water-jet pump.

A first aspect of the invention relates to an internal combustion engineexhaust cooling system that includes an exhaust gas cooling adapter thatis arranged between an exhaust port that opens in a cylinder head, andan exhaust branch pipe, and cools exhaust gas that flows through anexhaust passage by running coolant through a coolant passage formedinside of a wall that surrounds the exhaust passage. The exhaust gascooling adapter includes a coolant inlet that introduces coolant intothe coolant passage, and a coolant outlet that discharges coolantoutside from the coolant passage. The coolant passage includes a firstpassage that is on a high heat receiving side and a second passage thatis on a low heat receiving side, the first passage and the secondpassage being provided according to an offset of an amount of heatreceived from exhaust gas in a circumferential direction of an innersurface of the exhaust passage, and two middle passages that connect thefirst passage with the second passage at both ends of the two middlepassages. A coolant delivery direction of the coolant inlet is adirection from the second passage side of a first middle passage, of thetwo middle passages, toward the first passage side. Also, the coolantoutlet discharges coolant from a location where a second middle passage,of the two middle passages, is connected with the first passage, or fromnear the location.

With this internal combustion engine exhaust cooling system, in theexhaust gas cooling adapter, coolant that is delivered from the coolantinlet to the coolant passage immediately heads from the second passageside of the first middle passage, of the two middle passages, toward thefirst passage side.

As a result, the pressure of the coolant delivered from the coolantinlet is sufficiently transmitted to the first passage, while littlecoolant pressure is transmitted to the second passage. Thus, coolantflows faster in the first passage than it does in the second passage. Asa result, the flow rate of coolant that flows through the coolantpassage is greater in the first passage and smaller in the secondpassage, so the temperature at the exhaust passage portion on the firstpassage side that tends to increase can be inhibited from increasing.The exhaust passage portion on the second passage side essentially tendsnot to increase in temperature, so the temperature is able to beinhibited from increasing even if the coolant flow rate is reduced.

Therefore, the exhaust passage of the exhaust gas cooling adapter can beefficiently cooled without increasing the total coolant flow rate, sothe exhaust gas cooling adapter will not become larger and the load onthe water-jet pump will not increase.

A second aspect of the invention relates to an internal combustionengine exhaust cooling system that includes an exhaust gas coolingadapter that is arranged between an exhaust port that opens in acylinder head, and an exhaust branch pipe, and cools exhaust gas thatflows through an exhaust passage by running coolant through a coolantpassage formed inside of a wall that surrounds the exhaust passage. Theexhaust gas cooling adapter includes a coolant inlet that introducescoolant into the coolant passage, and a coolant outlet that dischargescoolant outside from the coolant passage. The coolant passage includesan outside passage of a curve and an inside passage of a curve that areprovided according to a curve in an exhaust flow produced by a curvedshape of the exhaust port, and two middle passages that connect theoutside passage with the inside passage at both ends of the two middlepassages. A coolant delivery direction of the coolant inlet is adirection from the inside passage side of a first middle passage, of thetwo middle passages, toward the outside passage side. Also, the coolantoutlet discharges coolant from a location where a second middle passage,of the two middle passages, is connected with the outside passage, orfrom near the location.

In this aspect, in the exhaust gas cooling adapter, coolant that isdelivered from the coolant inlet to the coolant passage immediatelyheads from the inside passage side of the first middle passage, of thetwo middle passages, toward the outside passage side.

As a result, the pressure of the coolant delivered from the coolantinlet is sufficiently transmitted to the first passage, while littlecoolant pressure is transmitted to the inside passage. Thus, coolantflows faster in the outside passage than it does in the inside passage,so the flow rate of coolant that flows through the coolant passage isgreater in the outside passage and smaller in the inside passage.

The exhaust port is curved, so a curve is produced in the exhaust flowuntil the exhaust gas reaches the exhaust gas cooling adapter.Therefore, in the exhaust gas cooling adapter, the inner surface of theexhaust passage that corresponds to the outside of the curve of theexhaust flow tends to increase in temperature due to the fast exhaustflow and the exhaust gas striking it.

In this internal combustion engine exhaust cooling system, as describedabove, the coolant flow rate is greater in the outside passage, that isa coolant passage that corresponds to an exhaust passage inner surfacethat tends to increase in temperature, than it is in the inside passage,so an increase in temperature at the exhaust passage portion that tendsto increase in temperature can be suppressed. The exhaust passageportion that corresponds to the inside passage essentially tends not toincrease in temperature, so the temperature is able to be inhibited fromincreasing even if the coolant flow rate is reduced.

Therefore, the exhaust passage of the exhaust gas cooling adapter can beefficiently cooled without increasing the total coolant flow rate, sothe exhaust gas cooling adapter will not become larger and the load onthe water-jet pump will not increase.

A third aspect of the invention relates to an internal combustion engineexhaust cooling system that includes an exhaust gas cooling adapter thatis arranged between an exhaust port that opens in a cylinder head, andan exhaust branch pipe, and cools exhaust gas that flows through anexhaust passage by running coolant through a coolant passage formedinside of a wall that surrounds the exhaust passage. The exhaust gascooling adapter includes a coolant inlet that introduces coolant intothe coolant passage, and a coolant outlet that discharges coolantoutside from the coolant passage. The coolant passage includes anoutside passage of a curve and an inside passage of a curve that areprovided according to a curve in an exhaust flow produced by a bentshape of a connecting portion between the exhaust port and the exhaustpassage, and two middle passages that connect the outside passage withthe inside passage at both ends of the two middle passages. A coolantdelivery direction of the coolant inlet is a direction from the insidepassage side of a first middle passage, of the two middle passages,toward the outside passage side. Also, the coolant outlet dischargescoolant from a location where a second middle passage, of the two middlepassages, is connected with the outside passage, or from near thelocation.

In this aspect, in the exhaust gas cooling adapter, coolant that isdelivered from the coolant inlet to the coolant passage immediatelyheads from the inside passage side of the first middle passage, of thetwo middle passages, toward the outside passage side.

As a result, the pressure of the coolant delivered from the coolantinlet is sufficiently transmitted to the outside passage, while littlecoolant pressure is transmitted to the inside passage. Thus, coolantflows faster in the outside passage than it does in the inside passage,so the flow rate of coolant that flows through the coolant passage isgreater in the outside passage and smaller in the inside passage.

The connecting portion of the exhaust port on the cylinder head side andthe exhaust passage of the exhaust gas cooling adapter is bent, so acurve is produced in the exhaust flow until the exhaust gas reaches theexhaust gas cooling adapter. Therefore, in the exhaust gas coolingadapter, the inner surface of the exhaust passage that corresponds tothe outside of the curve of the exhaust flow tends to increase intemperature due to the fast exhaust flow and the exhaust gas strikingit.

In the foregoing aspect, as described above, the coolant flow rate isgreater in the outside passage, that is a coolant passage thatcorresponds to an exhaust passage inner surface that tends to increasein temperature, than it is in the inside passage, so an increase intemperature at the exhaust passage portion that tends to increase intemperature can be suppressed. The exhaust passage portion thatcorresponds to the inside passage essentially tends not to increase intemperature, so the temperature is able to be inhibited from increasingeven if the coolant flow rate is reduced.

Therefore, the exhaust passage of the exhaust gas cooling adapter can beefficiently cooled without increasing the total coolant flow rate, sothe exhaust gas cooling adapter will not become larger and the load onthe water-jet pump will not increase.

In the aspect described above, the coolant outlet may discharge coolantin the same direction as a flow direction of coolant in the firstpassage.

Also, the coolant outlet is a passage that discharges coolant in thesame direction as the flow direction of coolant in the first passage.Therefore, the flow direction of coolant that has flowed through thefirst passage at a fast rate does not change when the coolant flows outto the coolant outlet. As a result, the flow resistance does notincrease when coolant is discharged from the coolant passage, so thefast coolant flow of the first passage is not impeded. Therefore, thecoolant flows more smoothly, which further increases the effects ofsuppressing the exhaust gas cooling adapter from becoming larger andsuppressing the load on the water-jet pump from increasing.

In the structure described above, the coolant outlet may dischargecoolant in the same direction as a flow direction of coolant in theoutside passage.

Also, the coolant outlet is a passage that discharges coolant in thesame direction as the flow direction of coolant in the outside passage.Therefore, the flow direction of coolant that has flowed through theoutside passage at a fast rate does not change when the coolant flowsout to the coolant outlet. As a result, the flow resistance does notincrease when coolant is discharged from the coolant passage, so thefast coolant flow of the outside passage is not impeded. Therefore, thecoolant flows more smoothly, which further increases the effects ofsuppressing the exhaust gas cooling adapter from becoming larger andsuppressing the load on the water-jet pump from increasing.

In the aspect described above, a plurality of the exhaust ports may beprovided, and each of the plurality of exhaust ports may be arranged andopen in a cylinder head. A plurality of the exhaust passages may beformed in an arrangement inside the exhaust gas cooling adapter, thearrangement of the plurality of exhaust passages corresponding to anarrangement of the plurality of exhaust ports. Further, the exhaustports may be formed curved in a direction orthogonal to an arrangementdirection of the exhaust passages, or the exhaust ports and the exhaustpassages may be connected bent in a direction orthogonal to thearrangement direction.

In this way, each of the exhaust ports in the cylinder head and theexhaust passages of the exhaust gas cooling adapter are arranged (i.e.,aligned), and, as described above, the exhaust ports are formed curvedin a direction orthogonal to the arrangement direction, or the exhaustports and the exhaust passages are connected bent in a directionorthogonal to the arrangement direction. With this kind of structure,the first passage or the outside passage, and the second passage or theinside passage, are formed along the arrangement direction, as describedabove.

Therefore, the coolant flow rate is increased on the side that tends toincrease in temperature, and the coolant flow rate is suppressed on theside that tends not to increase in temperature, as described above. As aresult, the exhaust passage of the exhaust gas cooling adapter can beefficiently cooled without increasing the total coolant flow rate, sothe exhaust gas cooling adapter will not become larger and the load onthe water-jet pump will not increase.

In the aspect described above, a plurality of the exhaust ports may beprovided, and each of the plurality of exhaust ports may be arranged andopen in a cylinder head. A plurality of the exhaust passages may beformed in an arrangement inside the exhaust gas cooling adapter, thearrangement of the plurality of exhaust passages corresponding to anarrangement of the plurality of exhaust ports. Further, the exhaustports may be formed curved in a direction orthogonal to an arrangementdirection of the exhaust passages, or the exhaust ports and the exhaustpassages may be connected bent in a direction orthogonal to thearrangement direction. Also, the coolant inlet may deliver coolant fromthe second passage toward the first passage via a middle passage on oneend side in the arrangement direction, and the coolant outlet maydischarge coolant from a location where a middle passage on the otherend side in the arrangement direction is connected to the first passage,or from near the location.

In this way, each of the exhaust ports in the cylinder head and theexhaust passages of the exhaust gas cooling adapter are arranged (i.e.,aligned), and, as described above, the exhaust ports are formed curvedin a direction orthogonal to the arrangement direction, or the exhaustports and the exhaust passages are connected bent in a directionorthogonal to the arrangement direction. With this kind of structure,the first passage and the second passage are formed along thearrangement direction, as described above.

Arranging the coolant inlet and the coolant outlet in this way withrespect to the first passage and the second passage makes it possible toincrease the coolant flow rate on the first passage side that tends toincrease in temperature, and suppress the coolant flow rate on thesecond passage side that tends not to increase in temperature, asdescribed above. As a result, the exhaust passage of the exhaust gascooling adapter can be efficiently cooled without increasing the totalcoolant flow rate, so the exhaust gas cooling adapter will not becomelarger and the load on the water-jet pump will not increase.

In the structure described above, a plurality of the exhaust ports maybe provided, and each of the plurality of exhaust ports may be arrangedand open in a cylinder head. A plurality of the exhaust passages may beformed in an arrangement inside the exhaust gas cooling adapter, thearrangement of the plurality of exhaust passages corresponding to anarrangement of the plurality of exhaust ports. Further, the exhaustports may be formed curved in a direction orthogonal to an arrangementdirection of the exhaust passages, or the exhaust ports and the exhaustpassages may be connected bent in a direction orthogonal to thearrangement direction. Also, the coolant inlet may deliver coolant fromthe inside passage toward the outside passage via a middle passage onone end side in the arrangement direction, and the coolant outlet maydischarge coolant from a location where a middle passage on the otherend side in the arrangement direction is connected to the outsidepassage, or from near the location.

In this way, each of the exhaust ports in the cylinder head and theexhaust passages of the exhaust gas cooling adapter are arranged (i.e.,aligned), and, as described above, the exhaust ports are formed curvedin a direction orthogonal to the arrangement direction, or the exhaustports and the exhaust passages are connected bent in a directionorthogonal to the arrangement direction. With this kind of structure,the outside passage and the inside passage are formed along thearrangement direction, as described above.

Arranging the coolant inlet and the coolant outlet in this way withrespect to the outside passage and the inside passage makes it possibleto increase the coolant flow rate on the outside passage side that tendsto increase in temperature, and suppress the coolant flow rate on theinside passage side that tends not to increase in temperature, asdescribed above. As a result, the exhaust passage of the exhaust gascooling adapter can be efficiently cooled without increasing the totalcoolant flow rate, so the exhaust gas cooling adapter will not becomelarger and the load on the water-jet pump will not increase.

In the structure described above, the arrangement direction of theexhaust ports in the cylinder head may be a horizontal direction, andthe direction orthogonal to the arrangement direction may be verticallydownward.

When the arrangement direction of the exhaust ports in the cylinder headand the exhaust passages of the exhaust gas cooling adapter are set andthe direction of the curve of the exhaust flow is set in this way, thecoolant flow rate in the coolant passage provided on the verticallyupper side and extending in the arrangement direction inside the exhaustgas cooling adapter (i.e., the first passage or the outside passage) isincreased. Also, the coolant flow rate in the coolant passage providedon the vertically lower side and extending in the arrangement direction(i.e., the second passage or the inside passage) is suppressed.Therefore, the exhaust passage of the exhaust gas cooling adapter can beefficiently cooled without increasing the total coolant flow rate, sothe exhaust gas cooling adapter will not become larger and the load onthe water-jet pump will not increase.

In the aspect described above, a flow direction guide that guides a flowof coolant delivered from the coolant inlet to a first middle passage,of the two middle passages, may be provided in the coolant passage, in alocation near the coolant inlet.

In this way, the flow direction guide that guides the flow of coolant toan appropriate middle passage may be provided in the coolant passage.Doing so makes it easy to appropriately split the flow of the coolantbetween the first passage and the second passage or between the outsidepassage and the inside passage, such that the flow rate becomes largerin the first passage or the outside passage.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, advantages, and technical and industrial significance ofthis invention will be described in the following detailed descriptionof example embodiments of the invention with reference to theaccompanying drawings, in which like numerals denote like elements, andwherein:

FIG. 1 is a longitudinal sectional view of an internal combustion engineexhaust cooling system according to a first example embodiment of theinvention;

FIGS. 2A and 2B are perspective views of an exhaust gas cooling adapterused in the internal combustion engine exhaust cooling system;

FIGS. 3A, 3B, and 3C are views of the structure of the exhaust gascooling adapter used in the internal combustion engine exhaust coolingsystem;

FIGS. 4A, 4B, and 4C are views of the structure of the exhaust gascooling adapter used in the internal combustion engine exhaust coolingsystem;

FIGS. 5A and 5B are views of the spatial configuration of the waterjacket inside the exhaust gas cooling adapter used in the internalcombustion engine exhaust cooling system;

FIGS. 6A, 6B, and 6C are sectional views of an exhaust gas coolingadapter used in an internal combustion engine exhaust cooling systemaccording to a second example embodiment of the invention; and

FIGS. 7A and 7B are sectional views of exhaust gas cooling adapters usedin internal combustion engine exhaust cooling systems according to otherexample embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS First Example Embodiment

FIG. 1 is a longitudinal sectional view of the structure of an exhaustcooling system 4 in an exhaust system of an internal combustion engine 2according to an example embodiment of the invention. This internalcombustion engine 2 is a V-type 6 cylinder gasoline engine mounted in avehicle, and has two banks, one arranged on the left and one arranged onthe right, with a bank angle of 60°. FIG. 1 shows the exhaust coolingsystem 4 of the right bank 6.

Intake air and fuel are introduced as an air-fuel mixture into acombustion chamber 6 b of a cylinder 6 a in the right bank 6 via anintake port 8 and an intake valve 10 from an intake system during anintake stroke. The air-fuel mixture is compressed by a piston 6 c duringa compression stroke, and ignited and combusted by a spark plug 6 dduring a combustion stroke. Then gas inside the combustion chamber 6 bis discharged as exhaust gas to the exhaust system by opening an exhaustvalve 12 during an exhaust stroke. Exhaust gas is also discharged to theexhaust system during the exhaust stroke from the other two cylinders ofthe right bank 6 and the three cylinders of the left bank as well.

Here, the exhaust system for the right bank 6 side includes an exhaustport 16 (i.e., a total of three exhaust ports for all of the cylindersof the right bank 6) formed in a cylinder head 14, an exhaust gascooling adapter 18 that is connected to the cylinder head 14 at theopening of the exhaust port 16, and an exhaust branch pipe 20 that isconnected to the exhaust gas cooling adapter 18. Other than these, anexhaust gas control catalyst and the like are provided downstream in theexhaust system of the right bank 6. The exhaust system of the left banksimilarly includes a total of three exhaust ports formed in the cylinderhead, an exhaust gas cooling adapter, and an exhaust branch pipe. Inthis example embodiment, the exhaust gas cooling adapter of the leftbank has the same structure as the exhaust gas cooling adapter 18 of theright bank 6. However, the positional relationship of the axis with theexhaust port side, the angle at which it is mounted to the cylinderhead, or the length or curved shape or the like may be different.

FIGS. 2 to 4 are views of the structure of the exhaust gas coolingadapter 18 of the exhaust system of the right bank 6. FIG. 2A is aperspective view from an exhaust inlet 22 side, and FIG. 2B is aperspective view from an exhaust outlet 24 side. FIG. 3A is a plan view,FIG. 3B is a front view, and FIG. 3C is a bottom view. FIG. 4A is a leftside view, FIG. 4B is a right side view, and FIG. 4C is a rear view.Incidentally, in FIGS. 2A and 2B, the spatial configuration of a waterjacket 34 on the inside is indicated by the broken line.

The exhaust gas cooling adapter 18 is arranged between the exhaust port16 that opens in the cylinder head 14 of the right bank 6 and theexhaust branch pipe 20, as shown in FIG. 1. The exhaust gas coolingadapter 18 cools exhaust gas discharged from the exhaust port 16 anddischarges the cooled exhaust gas to the exhaust branch pipe 20 side,thereby inhibiting heat damage to the exhaust system of the right bank6.

This kind of exhaust gas cooling adapter 18 is molded out of metalmaterial such as aluminum alloy or iron alloy, for example, and has acylinder head side connecting surface 28 with an open exhaust inlet 22formed on the exhaust upstream side. Three of these exhaust inlets 22are provided arranged in a straight line, corresponding to the positionand number of the exhaust ports 16 of the cylinder head 14 of the rightbank 6.

On the exhaust downstream side, an exhaust branch pipe side connectingsurface 30 with an open exhaust outlet 24 is formed. Three of theseexhaust outlets 24 are provided arranged in a straight line,corresponding to the exhaust inlets 22. Each exhaust inlet 22 isconnected to a corresponding exhaust outlet 24 by a correspondingexhaust passage 32 formed inside the exhaust gas cooling adapter 18.

Bolt fastening portions 28 a for fastening the exhaust gas coolingadapter 18 itself to an adapter connecting surface 14 a on the cylinderhead 14 side with bolts are formed on the exhaust gas cooling adapter 18at peripheral portions of the cylinder head side connecting surface 28.The exhaust gas cooling adapter 18 is fixed to the cylinder head 14 byinserting bolts into bolt insertion holes 28 b formed in the boltfastening portions 28 a and screwing them into threaded holes in theadapter connecting surface 14 a on the cylinder head 14 side. As aresult, the exhaust port 16 on the cylinder head 14 side can beconnected with the exhaust passage 32 on the exhaust gas cooling adapter18 side.

Moreover, bolt fastening portions 30 a for fastening the exhaust branchpipe 20 with bolts are formed on the exhaust gas cooling adapter 18 atperipheral portions of the exhaust branch pipe side connecting surface30. Threaded holes 30 b are formed in these bolt fastening portions 30a. The exhaust branch pipe 20 is connected by screwing in bolts throughinsertion holes formed in flanges 20 a on the exhaust branch pipe 20side. As a result, the exhaust passage 32 on the exhaust gas coolingadapter 18 side can be connected with the exhaust passage 20 b on theexhaust branch pipe 20 side.

In this way, a water jacket 34 is formed around the exhaust passage 32,inside the wall of the exhaust gas cooling adapter 18 that is mounted tothe internal combustion engine 2. FIGS. 5A and 5B are views of thespatial configuration of the water jacket 34 inside the exhaust gascooling adapter 18. FIGS. 5A and 5A is a perspective view from theexhaust inlet 22 side, and FIGS. 5A and 5B is a perspective view fromthe exhaust outlet 24 side.

As shown in FIGS. 2 to 4, a coolant introducing portion 36 is providedon the vertically lower side of the water jacket 34 on the exhaust gascooling adapter 18, and a coolant discharging portion 38 is provided onthe vertically upper side of the water jacket 34 in the exhaust gascooling adapter 18.

Coolant is introduced into the water jacket 34 from a coolant inlet 36 aformed in the coolant introducing portion 36, and after flowing throughthe water jacket 34, is discharged to an external coolant circulationpath via a coolant outlet 38 a formed in the coolant discharging portion38, as shown by the arrows in FIGS. 5A and 5B.

As a result, the amount of heat transmitted from high temperatureexhaust gas via inner peripheral surfaces 32 a and 32 b (FIG. 1) of theexhaust passage 32 is absorbed by the coolant flowing through coolantpassages 34 a, 34 b, 34 c, 34 d, and 34 e of the water jacket 34,thereby cooling the exhaust gas. The cooled exhaust gas is thendischarged to the exhaust branch pipe 20 side.

Here, as shown by the alternate long and short dash lines in FIG. 1, theaxis X1 of the exhaust port 16 is at an angle θ to the axis X2 of theexhaust passage 32. Instead of the axes X1 and X2 crossing each other,they may also be non-crossing and non-parallel by an angle θ.

In this example embodiment, the axis X2 of the exhaust passage 32 isbent vertically downward at an angle θ with respect to the axis X1 ofthe exhaust port 16. Therefore, the inner peripheral surface 32 a on thevertically upper side of the exhaust passage 32 forms an area thatslopes toward the exhaust port 16. The inner peripheral surface 32 b onthe vertically lower side is not an area that slopes toward the exhaustport 16, but instead slopes in the opposite direction, i.e., away fromthe exhaust port 16.

In this way, the inner peripheral surface 32 a on the vertically upperside of the exhaust passage 32 has a shape that slopes toward theexhaust port 16. Therefore, exhaust gas that has been introduced fromthe exhaust port 16 into the exhaust passage 32 of the exhaust gascooling adapter 18 strikes the inner peripheral surface 32 a on thevertically upper side comparatively harder than it strikes the innerperipheral surface 32 b on the vertically lower side.

Moreover, the exhaust port 16 extends in a curved shape from thecombustion chamber 6 b to the exhaust gas cooling adapter 18, and thevertically upper side is on the outside of the curve. Therefore, hightemperature exhaust flows faster at the inner peripheral surface 32 a onthe vertically upper side than it does at the inner peripheral surface32 b on the vertically lower side, so high temperature exhaust gasstrikes the inner peripheral surface 32 a on the vertically upper sidehard. Thus, the inner peripheral surface 32 a on the vertically upperside receives a particularly large amount of heat. That is, the innerperipheral surface 32 a on the vertically upper side is a high heatreceiving side and the inner peripheral surface 32 b on the verticallylower side is a low heat receiving side.

In this kind of flow state, high temperature exhaust gas transfers heatto the inner peripheral surfaces 32 a and 32 b, such that the exhaustgas itself is cooled, after which it flows out to the exhaust passage 20b on the exhaust branch pipe 20 side. Here, in the water jacket 34, theposition where coolant is introduced at the coolant inlet 36 a is aposition, near the coolant passage 34 b, of the coolant passage 34 dthat communicates the coolant passage 34 b on the vertically lower sidewith the coolant passage 34 a on the vertically upper side on one endside of the exhaust passages 32 in the direction in which the exhaustpassages 32 are arranged (also simply referred to as the “arrangementdirection”). The coolant inlet 36 a delivers coolant toward the coolantpassage 34 a on the vertically upper side from a position on the coolantpassage 34 b side that is on the vertically lower side.

That is, the direction in which coolant is delivered from the coolantinlet 36 a is the direction from the coolant passage 34 b side of thecoolant passage 34 d, that is one of the middle passages, toward thecoolant passage 34 a side. The coolant passage 34 b is on the verticallylower side and is a passage on the inside of the curve of the exhaustflow that follows the curve of the exhaust port 16 (the coolant passage34 b may also be referred to as an “inside passage” in thisspecification). The coolant passage 34 a, on the other hand, is on thevertically upper side and is a passage on the outside of the curve ofthe exhaust flow (the coolant passage 34 a may also be referred to as an“outside passage” in this specification).

Also, the direction in which coolant is delivered from the coolant inlet36 a is the direction from the coolant passage 34 b side of the coolantpassage 34 d, that is one of the middle passages, toward the coolantpassage 34 a side. The coolant passage 34 b is on the vertically lowerside and is a passage on the inside of the curve of the exhaust flowthat follows the bend at the connection of the exhaust port 16 and theexhaust passage 32 (the coolant passage 34 b may also be referred to asan “inside passage” in this specification). The coolant passage 34 a, onthe other hand, is on the vertically upper side and is a passage on theoutside of the curve of the exhaust flow (the coolant passage 34 a mayalso be referred to as an “outside passage” in this specification).

Therefore, coolant flows faster through the coolant passage 34 a that isthe outside passage than it does through the coolant passage 34 b thatis the inside passage. The following effects are able to be obtainedwith the first example embodiment described above.

As described above, the exhaust port 16 is curved in a directionorthogonal to the arrangement direction thereof. Moreover, theconnecting portion of the exhaust port 16 and the exhaust passage 32 ofthe exhaust gas cooling adapter 18 that is connected to the exhaust port16 is bent in a direction orthogonal to the arrangement direction. Thecurve and the bend are both vertically downward. In accordance withthis, the exhaust flow is in a direction that is orthogonal to thearrangement direction, and curves vertically downward.

As a result of this curve in the exhaust flow, the coolant passage 34 athat is formed in the arrangement direction in the exhaust gas coolingadapter 18 and arranged on the vertically upper side functions as afirst passage and an outside passage that corresponds to the innerperipheral surface 32 a on the high heat receiving side of the exhaustpassage 32. The coolant passage 34 b that is formed in the arrangementdirection and arranged on the vertically lower side functions as asecond passage and an inside passage that corresponds to the innerperipheral surface 32 b on the low heat receiving side of the exhaustpassage 32. Also, the two coolant passages 34 d and 34 e that connectthese coolant passages 34 a and 34 b together at the both ends functionas middle passages.

In this exhaust gas cooling adapter 18, the flow direction of coolantdelivered from the coolant inlet 36 a into the water jacket 34 is towardthe coolant passage 34 a side. Therefore, as shown by the arrows inFIGS. 5A and 5B, the main stream of the coolant flows through thecoolant passage 34 d that is the first middle passage of the two middlepassages (i.e., coolant passages 34 d and 34 e) from the coolant passage34 b side toward the coolant passage 34 a side. Accordingly, the amount(i.e., the flow rate) of coolant that flows toward the coolant passage34 b is small. Incidentally, in this example embodiment, the coolantpassage 34 d is located closer to the coolant inlet 36 than the coolantpassage 34 e is.

As a result, the pressure of the coolant delivered from the coolantinlet 36 a is sufficiently transmitted to the coolant passage 34 a,while little coolant pressure is transmitted to the coolant passage 34b. Thus, coolant flows faster in the coolant passage 34 a than it doesin the coolant passage 34 b. As a result, the flow rate of coolant thatflows through the water jacket 34 is greater in the coolant passage 34 aand smaller in the coolant passage 34 b, so the temperature at the innerperipheral surface 32 a on the vertically upper side of the exhaustpassage 32 that tends to increase can be inhibited from increasing.Therefore, resistance to boiling at the coolant passage 34 a as a resultof heat transfer from the inner peripheral surface 32 a can also beimproved.

The inner peripheral surface 32 b on the vertically lower sideessentially tends not to increase in temperature, so the temperature isable to be inhibited from increasing even if the coolant flow rate inthe corresponding coolant passage 34 b is reduced. In this way, theexhaust passage 32 of the exhaust gas cooling adapter 18 can beefficiently cooled without increasing the total flow rate of coolantthat flows through the water jacket 34, so the exhaust gas coolingadapter 18 will not become larger and the load on the water-jet pumpwill not increase.

Also, the coolant outlet 38 a is a passage that discharges coolant inthe same direction as the direction in which coolant flows (i.e., theflow direction of coolant) in the coolant passage 34 a. Therefore, asshown by the arrows in FIGS. 5A and 5B, the flow direction of coolantthat has flowed through the coolant passage 34 a at a fast rate does notchange when the coolant flows out to the coolant outlet 38 a. As aresult, the flow resistance does not increase when the coolant flows outof the coolant passage 34 a, so the fast coolant flow of the coolantpassage 34 a is not impeded.

Therefore, the coolant flows more smoothly, which further increases theeffects of suppressing the exhaust gas cooling adapter 18 from becominglarger and suppressing the load on the water-jet pump from increasing.

Second Example Embodiment

FIG. 6 is a sectional view of exhaust gas cooling adapters 118, 218, and318 used in an exhaust cooling system according to a second exampleembodiment of the invention. Incidentally, the other structure of theexhaust cooling system is the same as it is in the first exampleembodiment described above.

With the exhaust gas cooling adapter 118 shown in FIG. 6A, a coolantinlet 136 a of a coolant introducing portion 136 that introduces coolantinto a water jacket 134 opens into a coolant passage 134 b (thatfunctions as a second passage and an inside passage) that is arranged onthe vertically lower side and extends in the direction in which exhaustpassages 132 are arranged (i.e., in the arrangement direction of theexhaust passages 132), and delivers coolant into this coolant passage134 b.

A flow direction guide 136 b is formed on a side of an edge portion of aportion of the coolant inlet 136 a that opens to the coolant passage 134b side, that is opposite a coolant passage 134 d (that functions as amiddle passage) side. A tip end of this flow direction guide 136 bpoints toward the coolant passage 134 d side. Therefore, the pressure ofthe coolant that has been introduced from the coolant inlet 136 a intothe coolant passage 134 b is directed toward the coolant passage 134 dside by the flow direction guide 136 b.

As a result, as shown by the arrows in the drawing, the main stream ofthe coolant flows toward the coolant passage 134 d side, and the flowrate of this coolant is large. The flow rate of the coolant that flowsthrough the coolant passage 134 b toward the side with a coolant passage134 e that is a middle passage on the opposite side is small.

The flow of the coolant (i.e., the coolant pressure) in the coolantpassage 134 d turns directly into the flow in a coolant passage 134 a(that functions as a first passage and an outside passage) that isarranged on the vertically upper side and extends in the direction inwhich the exhaust passages 132 are arranged (i.e., the arrangementdirection of the exhaust passages 132), and then flows to a coolantdischarging portion 138.

The direction of a coolant outlet 138 a of the coolant dischargingportion 138 is the same as the direction of the coolant passage 134 a,so the coolant also flows inside the coolant outlet 138 a without losingany pressure, and is discharged outside as it is from the coolant outlet138 a.

With the exhaust gas cooling adapter 218 shown in FIG. 6B, a coolantinlet 236 a of a coolant introducing portion 236 that introduces coolantinto a water jacket 234 opens into a coolant passage 234 b (thatfunctions as a second passage and an inside passage) that is arranged onthe vertically lower side and extends in the direction in which exhaustpassages 232 are arranged (i.e., in the arrangement direction of theexhaust passages 232), and delivers the coolant into this coolantpassage 234 b, similar to FIG. 6A.

However, in the example shown in FIG. 6B, a flow direction guide 236 bis formed on a wall portion side of an opposing exhaust passage 232,instead of on an edge portion of the coolant inlet 236 a. A tip end ofthis flow direction guide 236 b is formed pointed toward an edge portionof the coolant inlet 236 a, that is on the side opposite a coolantpassage 234 d (that functions as a middle passage) side.

Accordingly, the pressure of the coolant that has been introduced fromthe coolant inlet 236 a into the coolant passage 234 b is directedtoward the coolant passage 234 d side by the sloped surface of the flowdirection guide 236 b. As a result, as shown by the arrows in thedrawing, the main stream of the coolant flows toward the coolant passage234 d side, and the flow rate of this coolant is large. The flow rate ofthe coolant that flows through the coolant passage 234 b toward the sidewith a coolant passage 234 e that is a middle passage on the oppositeside is small.

The flow of the coolant (i.e., the coolant pressure) in this coolantpassage 234 d turns directly into the flow in a coolant passage 234 a(that functions as a first passage and an outside passage) that isarranged on the vertically upper side and extends in the direction inwhich the exhaust passages 232 are arranged (i.e., the arrangementdirection of the exhaust passages 232), and then flows to a coolantdischarging portion 238.

The direction of a coolant outlet 238 a of the coolant dischargingportion 238 is the same as the direction of the coolant passage 234 a,so the coolant flows without losing any pressure, and is dischargedoutside as it is from the coolant outlet 238 a.

With the exhaust gas cooling adapter 318 shown in FIG. 6C, a coolantinlet 336 a of a coolant introducing portion 336 that introduces coolantinto a water jacket 334 opens into a coolant passage 334 b (thatfunctions as a second passage and an inside passage) that is arranged onthe vertically lower side and extends in the direction in which exhaustpassages 332 are arranged (i.e., in the arrangement direction of theexhaust passages 332), and delivers the coolant into this coolantpassage 334 b. This is the same as in FIG. 6A.

However, compared with FIG. 6A, the coolant inlet 336 a of the coolantintroducing portion 336 is farther away from a coolant passage 334 d(that functions as a middle passage) and is provided in a positionfacing a coolant passage 334 c that connects a coolant passage 334 a(that functions as a first passage and an outside passage) with thecoolant passage 334 b at a center portion. Therefore, a flow directionguide 336 b that is formed on an opening edge portion of a coolant inlet336 a on the side opposite the coolant passage 334 d (that functions asa middle passage) is formed longer and extending toward the coolantpassage 334 d side, such that sufficient coolant pressure reliablyreaches the coolant passage 334 d.

As a result, as shown by the arrows in the drawing, the main stream ofthe coolant flows toward the coolant passage 334 d side, and the flowrate of this coolant is large. The flow rate of the coolant that flowsthrough the coolant passage 334 b toward the side with a coolant passage334 e that is a middle passage on the opposite side is small.

The flow of the coolant (i.e., the coolant pressure) in the coolantpassage 334 d turns directly into the flow in a coolant passage 334 athat is arranged on the vertically upper side and extends in thedirection in which the exhaust passages 332 are arranged (i.e., in thearrangement direction of the exhaust passages 332), and then flows to acoolant discharging portion 338.

The direction of a coolant outlet 338 a of the coolant dischargingportion 338 is the same as the direction of the coolant passage 334 a,so the coolant flows without losing any pressure, and is dischargedoutside as it is from the coolant outlet 338 a.

The following effects are able to be obtained with the second exampleembodiment described above. The main flow of coolant is able to bedirected toward the coolant passage 134 a, 234 a, or 334 a via thecoolant passage 134 d, 234 d, or 334 d by the flow direction guide 136b, 236 b, or 336 b also when the coolant introducing portion 136, 236,or 336 is mounted on the coolant passage 134 b, 234 b, or 334 b side inthis way.

As a result, effects similar to those described in the first exampleembodiment are able to be obtained.

Other Example Embodiments

With an exhaust gas cooling adapter 418 shown in FIG. 7A, when a coolantinlet 436 a of a coolant introducing portion 436 is connected to acoolant passage 434 b that functions as a second passage and an insidepassage, the coolant inlet 436 a may be formed at an angle such that themain stream of coolant is directed toward a coolant passage 434 d thatis a middle passage, instead of using a flow direction guide.

As a result, as shown by the arrows in the drawing, the flow of thecoolant (i.e., the coolant pressure) in the coolant passage 434 d turnsdirectly into the flow in a coolant passage 434 a that functions as afirst passage and an outside passage, and then flows to a coolantdischarging portion 438. The coolant then flows without losing anypressure, and is discharged outside as it is from a coolant outlet 438a. This structure also enables effects similar to those obtained in thefirst example embodiment to be obtained.

In the foregoing example embodiments, the direction of the coolantoutlet of the coolant discharging portion follows the flow direction ofcoolant in the coolant passage that functions as the first passage andthe outside passage. Alternatively, however, the direction of a coolantoutlet 538 a of a coolant discharging portion 538 may be a directionthat is different from the flow direction of coolant in a coolantpassage 534 a that functions as a first passage and an outside passage,as shown in FIG. 7B. In the example shown in FIG. 7B, the direction ofthe coolant outlet 538 a is a direction that is orthogonal to the flowdirection of coolant in the coolant passage 534 a. With this structureas well, the pressure of coolant delivered from a coolant inlet 536 a ofa coolant introducing portion 536 is transmitted to the coolant passage534 a via a coolant passage 534 d that serves as a middle passage, so asufficiently large coolant flow rate is able to be ensured in thecoolant passage 534 a. As a result, effects similar to those obtained inthe first example embodiment are able to be obtained.

Even if the exhaust port and the exhaust passage of the exhaust coolingadaptor are not bent, and there is only the curve of the exhaust port,the inner peripheral surface of the exhaust passage of the exhaust gascooling adapter that is on the outside of the curve will become the hightemperature receiving side, and the coolant passage that corresponds tothis inner peripheral surface will become the first passage. Therefore,the effects described above can be obtained by having coolant flow inthe manner described in the example embodiments described above.

Incidentally, even if only the connecting portion of the exhaust portand the exhaust passage of the exhaust gas cooling adapter is bent, theinner peripheral surface of the exhaust passage of the exhaust gascooling adapter that is on the outside of the bend will become the hightemperature receiving side, and the coolant passage that corresponds tothis inner peripheral surface will become the first passage. Therefore,the effects described above can be obtained by having coolant flow inthe manner described in the example embodiments described above.

FIG. 1 is a view of an example in which the invention is applied to aV-type 6 cylinder internal combustion engine. However, the invention mayalso be applied to an engine having in-line configuration, as well as toan engine with a number of cylinders other than six, such as fourcylinders or eight cylinders or the like.

1. An internal combustion engine exhaust cooling system comprising: anexhaust gas cooling adapter that is arranged between an exhaust portthat opens in a cylinder head, and an exhaust branch pipe, and coolsexhaust gas that flows through an exhaust passage by running coolantthrough a coolant passage formed inside of a wall that surrounds theexhaust passage, wherein the exhaust gas cooling adapter includes acoolant inlet that introduces coolant into the coolant passage, and acoolant outlet that discharges coolant outside from the coolant passage;the coolant passage includes a first passage that is on a high heatreceiving side and a second passage that is on a low heat receivingside, the first passage and the second passage being provided accordingto an offset of an amount of heat received from exhaust gas in acircumferential direction of an inner surface of the exhaust passage,and two middle passages that connect the first passage with the secondpassage at both ends of the two middle passages; a coolant deliverydirection of the coolant inlet is a direction from the second passageside of a first middle passage, of the two middle passages, toward thefirst passage side; and the coolant outlet discharges coolant from alocation where a second middle passage, of the two middle passages, isconnected with the first passage, or from near the location.
 2. Theinternal combustion engine exhaust cooling system according to claim 1,wherein the first middle passage is located closer to the coolant inletthan the second middle passage is.
 3. The internal combustion engineexhaust cooling system according to claim 1, wherein the coolant outletdischarges coolant in the same direction as a flow direction of coolantin the first passage.
 4. The internal combustion engine exhaust coolingsystem according to claim 1, wherein a plurality of the exhaust portsare provided; each of the plurality of exhaust ports is arranged andopen in a cylinder head; a plurality of the exhaust passages are formedin an arrangement inside the exhaust gas cooling adapter, thearrangement of the plurality of exhaust passages corresponding to anarrangement of the plurality of exhaust ports; and the exhaust ports areformed curved in a direction orthogonal to an arrangement direction ofthe exhaust passages, or the exhaust ports and the exhaust passages areconnected bent in a direction orthogonal to the arrangement direction.5. The internal combustion engine exhaust cooling system according toclaim 4, wherein the arrangement direction of the exhaust ports in thecylinder head is a horizontal direction, and the direction orthogonal tothe arrangement direction is vertically downward.
 6. The internalcombustion engine exhaust cooling system according to claim 1, wherein aplurality of the exhaust ports are provided; each of the plurality ofexhaust ports is arranged and open in a cylinder head; a plurality ofthe exhaust passages are formed in an arrangement inside the exhaust gascooling adapter, the arrangement of the plurality of exhaust passagescorresponding to an arrangement of the plurality of exhaust ports; theexhaust ports are formed curved in a direction orthogonal to anarrangement direction of the exhaust passages, or the exhaust ports andthe exhaust passages are connected bent in a direction orthogonal to thearrangement direction; the coolant inlet delivers coolant from thesecond passage toward the first passage via a middle passage on one endside in the arrangement direction; and the coolant outlet dischargescoolant from a location where a middle passage on the other end side inthe arrangement direction is connected to the first passage, or fromnear the location.
 7. The internal combustion engine exhaust coolingsystem according to claim 1, wherein a flow direction guide that guidesa flow of coolant delivered from the coolant inlet to a first middlepassage, of the two middle passages, is provided in the coolant passage,in a location near the coolant inlet.
 8. An internal combustion engineexhaust cooling system comprising: an exhaust gas cooling adapter thatis arranged between an exhaust port that opens in a cylinder head, andan exhaust branch pipe, and cools exhaust gas that flows through anexhaust passage by running coolant through a coolant passage formedinside of a wall that surrounds the exhaust passage, wherein the exhaustgas cooling adapter includes a coolant inlet that introduces coolantinto the coolant passage, and a coolant outlet that discharges coolantoutside from the coolant passage; the coolant passage includes anoutside passage of a curve and an inside passage of a curve that areprovided according to a curve in an exhaust flow produced by a curvedshape of the exhaust port, and two middle passages that connect theoutside passage with the inside passage at both ends of the two middlepassages; a coolant delivery direction of the coolant inlet is adirection from the inside passage side of a first middle passage, of thetwo middle passages, toward the outside passage side; and the coolantoutlet discharges coolant from a location where a second middle passage,of the two middle passages, is connected with the outside passage, orfrom near the location.
 9. The internal combustion engine exhaustcooling system according to claim 8, wherein the first middle passage islocated closer to the coolant inlet than the second middle passage. 10.The internal combustion engine exhaust cooling system according to claim8, wherein the exhaust passage is bent with respect to the exhaust port.11. The internal combustion engine exhaust cooling system according toclaim 8, wherein the coolant outlet discharges coolant in the samedirection as a flow direction of coolant in the outside passage.
 12. Theinternal combustion engine exhaust cooling system according to claim 8,wherein a plurality of the exhaust ports are provided; each of theplurality of exhaust ports is arranged and open in a cylinder head; aplurality of the exhaust passages are formed in an arrangement insidethe exhaust gas cooling adapter, the arrangement of the plurality ofexhaust passages corresponding to an arrangement of the plurality ofexhaust ports; and the exhaust ports are formed curved in a directionorthogonal to an arrangement direction of the exhaust passages, or theexhaust ports and the exhaust passages are connected bent in a directionorthogonal to the arrangement direction.
 13. The internal combustionengine exhaust cooling system according to claim 12, wherein thearrangement direction of the exhaust ports in the cylinder head is ahorizontal direction, and the direction orthogonal to the arrangementdirection is vertically downward.
 14. The internal combustion engineexhaust cooling system according to claim 8, wherein a plurality of theexhaust ports are provided; each of the plurality of exhaust ports isarranged and open in a cylinder head; a plurality of the exhaustpassages are formed in an arrangement inside the exhaust gas coolingadapter, the arrangement of the plurality of exhaust passagescorresponding to an arrangement of the plurality of exhaust ports; theexhaust ports are formed curved in a direction orthogonal to anarrangement direction of the exhaust passages, or the exhaust ports andthe exhaust passages are connected bent in a direction orthogonal to thearrangement direction; the coolant inlet delivers coolant from theinside passage toward the outside passage via a middle passage on oneend side in the arrangement direction; and the coolant outlet dischargescoolant from a location where a middle passage on the other end side inthe arrangement direction is connected to the outside passage, or fromnear the location.
 15. The internal combustion engine exhaust coolingsystem according to claim 8, wherein a flow direction guide that guidesa flow of coolant delivered from the coolant inlet to a first middlepassage, of the two middle passages, is provided in the coolant passage,in a location near the coolant inlet.
 16. An internal combustion engineexhaust cooling system comprising: an exhaust gas cooling adapter thatis arranged between an exhaust port that opens in a cylinder head, andan exhaust branch pipe, and cools exhaust gas that flows through anexhaust passage by running coolant through a coolant passage formedinside of a wall that surrounds the exhaust passage, wherein the exhaustgas cooling adapter includes a coolant inlet that introduces coolantinto the coolant passage, and a coolant outlet that discharges coolantoutside from the coolant passage; the coolant passage includes anoutside passage of a curve and an inside passage of a curve that areprovided according to a curve in an exhaust flow produced by a bentshape of a connecting portion between the exhaust port and the exhaustpassage, and two middle passages that connect the outside passage withthe inside passage at both ends of the two middle passages; a coolantdelivery direction of the coolant inlet is a direction from the insidepassage side of a first middle passage, of the two middle passages,toward the outside passage side; and the coolant outlet dischargescoolant from a location where a second middle passage, of the two middlepassages, is connected with the outside passage, or from near thelocation.
 17. The internal combustion engine exhaust cooling systemaccording to claim 16, wherein the first middle passage is locatedcloser to the coolant inlet than the second middle passage.
 18. Theinternal combustion engine exhaust cooling system according to claim 16,wherein a plurality of the exhaust ports are provided; each of theplurality of exhaust ports is arranged and open in a cylinder head; aplurality of the exhaust passages are formed in an arrangement insidethe exhaust gas cooling adapter, the arrangement of the plurality ofexhaust passages corresponding to an arrangement of the plurality ofexhaust ports; and the exhaust ports are formed curved in a directionorthogonal to an arrangement direction of the exhaust passages, or theexhaust ports and the exhaust passages are connected bent in a directionorthogonal to the arrangement direction.
 19. The internal combustionengine exhaust cooling system according to claim 18, wherein thearrangement direction of the exhaust ports in the cylinder head is ahorizontal direction, and the direction orthogonal to the arrangementdirection is vertically downward.
 20. The internal combustion engineexhaust cooling system according to claim 16, wherein a plurality of theexhaust ports are provided; each of the plurality of exhaust ports isarranged and open in a cylinder head; a plurality of the exhaustpassages are formed in an arrangement inside the exhaust gas coolingadapter, the arrangement of the plurality of exhaust passagescorresponding to an arrangement of the plurality of exhaust ports; theexhaust ports are formed curved in a direction orthogonal to anarrangement direction of the exhaust passages, or the exhaust ports andthe exhaust passages are connected bent in a direction orthogonal to thearrangement direction; the coolant inlet delivers coolant from theinside passage toward the outside passage via a middle passage on oneend side in the arrangement direction; and the coolant outlet dischargescoolant from a location where a middle passage on the other end side inthe arrangement direction is connected to the outside passage, or fromnear the location.
 21. The internal combustion engine exhaust coolingsystem according to claim 16, wherein a flow direction guide that guidesa flow of coolant delivered from the coolant inlet to a first middlepassage, of the two middle passages, is provided in the coolant passage,in a location near the coolant inlet.